The field of graphics processing applications, including image-processing packages, has broadened and matured to a point where many image processing programs and tools are capable of adjusting an array of image characteristics. Broadly speaking, many of these adjustments revolve around altering the color composition of a digital photograph or other image, or the exposure or lighting characteristics of the subject image or file. Within each category of task, commercially available programs typically offer a number of tools that change the relative amounts of red, green or blue (RGB) components or cyan, magenta, yellow or black (CMYK) component color in the pixels of an image.
To alter the color composition of an image, the color values associated with the image's pixels must undergo a transformation operation. These transformations may be referred to as effects. Certain effects use linear operations to alter the pixel values. For example, a levels effect uses a first-order curve with a linear slope to alter pixel data. As another example of a linear operation, a channel mixer effect is a three-dimensional matrix channel mapping of colors.
Non-linear operations may also be used to alter the color composition of an image. For example, curve effects are non-linear, single pixel channel transforms. These curve effects map each pixel's RGB channel data to new values based on a one-dimensional mapping or “curve.” There are usually independent curves for each channel. So, for a single curve effect, there may be a different curve for the red, green and blue color channels. Curve effects may be used with controls for altering contrast, brightness, saturation or exposure.
An effect pipeline is often used to make modifications to an image. As known to those skilled in the art, an effect pipeline relates to a series of sequentially performed image-processing steps. The effect pipeline is generally designed to allow efficient processing of a digital image, while taking advantage of available hardware. For example, the pipeline may perform significant operations on a dedicated graphics processor unit (GPU). Effects pipelines today are used to dynamically modify image data “non-destructively.” “Non-destructive editing” or “non-destructive processing” refers to editing (or processing) wherein rendering takes place beginning from unaltered originally-loaded image data. Each time a change is made, the alteration is added as one or more adjustments (or effects) added to the end of the pipeline. Hence the pipeline reflects the revision history (or progeny) of the image.
One limitation of conventional effect pipelines is that the non-destructive editing approach does not scale. In long effect pipelines, the application of curve effects can greatly increase delay and processing time. This result is exacerbated when adjustments are applied to effects near the beginning of the pipeline. As each subsequent effect needs to be re-applied for each render, the delay may be roughly proportional to the number of effects involved. To mitigate this delay, the adjacent linear operations may be aggregated into a single process. As known to those skilled in the art, linear operations can be easily combined into a single operation to enhance performance. When linear adjustments are not adjacent, the pipeline can often be re-ordered to aggregate them together. However, curve effects cannot be so easily combined. In fact, there are currently no techniques in the art for aggregating arbitrary non-linear pixel effects or even arbitrary non-linear ‘curve’ effects. Accordingly, multiple curve effects decrease performance in an effect pipeline and cause delays that are often noticeable to a user—often so much so that it makes non-destructive processing models impractical.